Fuels based on biocomponent sources will likely become increasingly prevalent in the future. Already, various governments have instituted current and future requirements that motor fuel pools contain a minimum percentage of fuel derived from a biocomponent source, such as a plant, animal, fish, or algae-based oil or fat.
Producing diesel fuel from biocomponent sources also presents a variety of challenges. In particular, for diesel hydroprocessing units that operate at low pressures, the presence of the additional heteroatoms in a biocomponent based diesel feed may pose difficulties. Modifying and/or replacing low pressure units to allow for higher processing pressures would require expensive capital investment.
For production of diesel fuel, vegetable oils such as canola oil, palm oil, or other similar oils have been identified as potentially suitable based on the carbon chain length of the vegetable oil. While some progress has been made toward stand alone processing and/or co-processing of biocomponent feeds, improvements to allow efficient processing in a refinery setting are greatly desired.
U.S. Patent Application Publication No. 2008/0154073 describes a process for removing oxygen from biocomponent molecules at low hydrogen pressure. The feed in this reference is exposed to a supported hydrogenation catalyst, such as Ni, NiMo, Pt, or Pd, in the presence of 150-290 psi hydrogen.
U.S. Patent Application Publication No. 2008/0161614 describes two stage co-processing of a feed including both vegetable/animal and mineral oil. According to this disclosure, the first stage is operated at lower severity to primarily treat the vegetable and/or animal oil in the feed. The product of the first stage is then stripped to remove gas phase impurities. The stripped product is then hydrotreated in a more severe hydrotreatment stage to produce a diesel fuel.
International Publication No. WO 2008/040980 describes reducing hydrogen consumption by controlling the products from reactions to remove oxygen from biocomponent feeds. Lower hydrogen pressures are mentioned as helping to reduce hydrogen consumption, but such pressures are mentioned as also leading to catalyst deactivation.
International Publication No. WO 2008/020048 describes a process for production of normal alkanes by hydrotreating mixtures of triglycerides or free fatty acids with vacuum gasoil. Conventional hydrotreatment catalysts are used in this process, which takes place at relatively mild conditions including a reaction pressure below 100 bars.
European Patent No. EP 1719811 describes a method for producing liquid hydrocarbons from biomass. The method includes forming an aqueous slurry of the biomass and particles of a layered catalyst, such as a clay. The slurry is heated to a temperature of 250-400° C. Up to 10 bars of hydrogen may optionally be added, although the publication indicates a preference to perform the process without added hydrogen.
European Patent No. EP 1741767 describes a process for producing diesel fuel from biocomponent sources. This reference states that the process reduces the needed hydrogen consumption by adding sulfur-containing compound to the biocomponent feed.
European Patent No. EP 1693432 describes co-processing of vegetable oils with various diesel type mineral refinery feeds. The method appears to include combining vegetable oil and mineral oil, hydrotreating the combined oil, and stripping off gas phase products.